Many are reporting nice eCPM values with
MobileCore, however you can't manually control ad caching (it just downloads everything at startup, which can be annoying when you use several ad networks) and for some reason their interstitial "lags" a lot when you press the close button. Also I've seen a grand total of 1 (repeated) ad two days ago and 1 ad yesterday even after calling refresh, which is terrible considering that I don't live in Zimbabwe but Italy.
AppNext looks great, their ads are clean and beautiful. Unfortunately I have only integrated it two days ago allocating 10% of my inventory, so the awful 0.38$ eCPM (compared to
AdMob's 1.50$+) doesn't really mean anything with just 10.000 impressions - too soon to have stable data, I'll keep it in the rotation for a while.